96 Chevy Tahoe Transmission issues

Michael Shane Decker · May 6, 2015

I have a 96 Chevy Tahoe SS. I had the transmission rebuilt last year. I keep having to take the vehicle back for a code p1870. The business has hade me replace the thermostat in the engine because they said my Tahoe wasnt running hot enough so it was causing it to make the transmission not work properly. They also had me replace the throttle position sensor. Well the vehicle is still having the same issue. The Tahoe seems to drive fine when you are just slowly taking off and cruising. If you happen to get on the vehicle a bit the engine RPMS jump up but its like the transmission is in nuetral, then a moment later it will kick in and go. The transmission shop is now trying to tell me that it might be the engine computer. They are going to replace the torque converter this week. If the vehicle still has the same problem they are telling me i now will need to replace the computer. Anyone have any suggestions?

Michael Shane Decker · May 7, 2015

@Doug Honestly, im not really sure. This Tahoe is my wifes vehicle. Until recently (the past few weeks) i never drove it. I prefer to drive my 3/4 ton chevy truck. I just happened to get in the vehicle a while back when we were camping and noticed the "Service Engine" light on. Of course i asked my wife about it and she had no clue when it came on or how long it has been on. So thats when i started to drive it more because i knew the warranty from the transmission shop is close to being over. The shop has the vehicle atm replacing the Torque converter. Not sure when i will get it back. The shop is about 46 miles from my home one way. Last week when i picked my vehicle up from the shop the transmission seemed to be fine up until about half way home. The service engine light lit up, and shortly after that I had a vehicle infront of me stop to turn. When i slowed down then went to give the vehicle gas to speed back up is when the transmission acted like it was in nuetral, the engine RPMs went up but the vehicle did not speed up. I let off the gas then put my foot back on the pedal and it switched gears and went again. I have not tried placing it in 1st, 2nd, or 3rd gear. I always just put it in drive and takeoff. The transmission was rebuilt almost a year ago. The vehicle has been back to the shop about 5 times now. We have only put roughly 5k miles on the transmission in the year that it has been replaced. A few of the people i work with have told me i should take it to another transmission shop and let them know what is going on with the vehicle just to see what they have to say about it. From what i am reading from your response and govtech4 i should probably take it to the dealership and have them check it out?

Thanks

Michael

Doug_Scott · May 7, 2015

The reason I mention trying manual low gear (shifter in 1) is due to manual low gives you engine braking. What you just described is exactly what I was asking about.

When truck is in drive and you slow down for a turn the transmission will downshift to the appropriate gear. If slow enough it will downshift to low gear(1st). Since there is no engine braking when low gear is applied this way, the engine will drop to idle speed. Once you step on the gas to go, the engine will have to rev up to catch up to the transmission. For example, if you are still traveling at 20mph, and when in low at 20mph the engine speed is usually 2500rpm, when you go to accelerate after the turn the engine must speed up to 2500 to catch up to the transmission. Let off the gas, engine drops to idle.

While the behavior is how it works, you should not be getting this. The tune in the transmission sounds too aggressive to me.

Again, this is just my interpretation of what you are reporting.

gmtech4 · May 7, 2015

I have a 96 Chevy Tahoe SS. I had the transmission rebuilt last year. I keep having to take the vehicle back for a code p1870. The business has hade me replace the thermostat in the engine because they said my Tahoe wasnt running hot enough so it was causing it to make the transmission not work properly. They also had me replace the throttle position sensor. Well the vehicle is still having the same issue. The Tahoe seems to drive fine when you are just slowly taking off and cruising. If you happen to get on the vehicle a bit the engine RPMS jump up but its like the transmission is in nuetral, then a moment later it will kick in and go. The transmission shop is now trying to tell me that it might be the engine computer. They are going to replace the torque converter this week. If the vehicle still has the same problem they are telling me i now will need to replace the computer. Anyone have any suggestions?

What Doug said ^^^^^^

They are idiots and DONT YOU DARE do another thing they say !!!! You hear me ?????

It needs to diagnosed and then they can pay for it ,,,,,,, the code has to be gone thru , they are a bitch to do but training of a GM tech will fix it ..... Sorry

Doug_Scott · May 6, 2015

Something I was told by the 64 year old transmission mechanic that trained me(back in 1977) was that torque converters do not fail like that. This was just before Chrysler released lockup converters. Torque converters are either there, or not. The very basic operation of them is most evident on drive off from dead stop. There are no variable moving parts involved, it is just two fans facing each other with a part between that becomes important once you hit rotary flow.

You need to describe this a bit better. Is this from a dead stop? Does it do this if the shift lever is in manual low or 1 gear(as opposed to Drive)? From what I can find, the p1870 means Transmission Component Slipping. It is kind of hard for the PCM to be slipping since it is bolted down, and does not even have any moving parts to slip. This sounds more like the transmission shop does not have experienced technicians in the model of your transmission.